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An Introduction to Perl

March 2001 Hesham Wahby Mentor Graphics Egypt. An Introduction to Perl. Presentation Outline. Introduction Hello world Basic Perl language Regular expressions Some common Perl functions A glimpse of some advanced features Conclusion. Introduction: What is Perl?.

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An Introduction to Perl

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  1. March 2001 Hesham Wahby Mentor Graphics Egypt An Introduction toPerl

  2. Presentation Outline • Introduction • Hello world • Basic Perl language • Regular expressions • Some common Perl functions • A glimpse of some advanced features • Conclusion

  3. Introduction:What is Perl? • Practical Extraction and Report Language. • Created in 1987 by Larry Wall, now maintained by hundreds of people. • A high-level programming/scripting language, combining features from C, Sed, Awk, Unix shells and many others. • Originally designed for text (and binary) string processing. • "Perl is designed to make the easy jobs easy and the hard jobs possible." • Perl motto: "There's more than one way to do it." • "Pathologically Eclectic Rubbish Lister"?

  4. Introduction:Features of Perl • Language features: • Simple to start using. Very rich set of tools. • Basically function oriented, with OO extensions. • C-style program structure. Free-style command syntax. • Weakly-typed variables. Implicit declaration. Sophisticated data structures. • Built-in regular expressions. • Built-in database access. • POSIX compliant. • Extensible using modules.

  5. Introduction:Features of Perl • Compiler features: • Compiled at load-time. • Can be translated to optimized C code. • Can also be directly integrated with other C/C++ code by either calling it or getting called by it. • Built-in debugger.

  6. Introduction:Getting Perl • Perl is GPL: freely distributable, open-source. • Where to get Perl: • The Perl Homepage: http://www.perl.com/ • CPAN (Comprehensive Perl Archive Network): http://www.cpan.org/ • ActivePerl Homepage (for Win32): http://www.activestate.com/ActivePerl/

  7. Hello world! • Example Perl program: "hello.pl": #!/usr/mgc/bin/perl print "Hello world! " • Command line: > perl hello.pl Hello world! > • To run as executable: > chmod +x hello.pl > ./hello.pl

  8. Hello world:Command-line options > perl[options] program.pl program_arguments > perl -e '$x=7; print 23*$x; print "\n"' > preprocess test.pl | perl > perl -h > perl -v > perl -w program.pl > perl -d program.pl > perl -c program.pl > perl -Ipath_for_modules program.pl > perl -Mmodule_name program.pl

  9. Hello world:A more extensive example • #!/usr/mgc/bin/perl • %types = (int => 'Integers', float => 'Reals'); • open INFILE, $ARGV[0]; • @lines = <INFILE>; • close INFILE; • # Search for variables • foreach (@lines) { • if (/^\s*(int|float)\s*(\w*)/) { • push @list[$1], $2; • } • } • $" = ', '; # Print them out • foreach $type (keys %list) { • print "$types[$type]: @list[$type].\n" • }

  10. Basic Perl language:Data types • Scalars $var • Lists (Arrays) @var $var[n] • Hashes (Associative arrays) %var $var[???] • Complex data structures

  11. Basic Perl language:Special variables • Default argument: $_ • Input record separator: $/ • Output field separator: $, • List separator: $" • Process Id: $$ • Program name: $0 • Command-line arguments: @ARGV • Subroutine arguments: @_ • Environment variables: %ENV

  12. Basic Perl language:Context $a = 'Take'; $x = 2; $y = '007'; @list = ('red','green','blue'); print $a . ' ' . $x; $b = "Take $x\n"; $z = $x + $y; $c = "$x + $y"; print "@list", @list, $#list; $i = @list; print $i; print $list[2]; print $list; $listLen = ("purple", @list, 'yellow', @list+2); $, = "\n"; print %ENV; print (keys %ENV); print (values %ENV);

  13. Basic Perl Language:Control constructs if (expression) {block} if (expression) {block} else {block} if (expression) {block} elsif (expression) {block} elsif (expression) {block} ... else {block} unless (expression) {block} unless (expression) {block} else {block}

  14. Basic Perl Language:Control constructs while (expression) {block} while (expression) {block} continue {block} do {block} while (expression); until (expression) {block} for (statement; expression; statement) {block} foreach variable (list) {block} label: goto label;

  15. Basic Perl language:File-handling • Opening a file: open FILE, $file #input open FILE, "<$file"; #input open (FILE, ">$file"); #output open FILE, ">>$file"; #append • Closing a file: close FILE; • Reading from a file: $line = <FILE>; @lines = <FILE>; read FILE, $data, 78, 10; • Writing to a file: print FILE "String.\n"; • Binary files: binmode FILE; • Reading output of a command-line: $output = `ls -l $dir`

  16. Basic Perl language:Subroutines sub Add { local ($x, $sum); $sum = 0; foreach $x (@_) { $sum += $x; } $sum; } $test = &Add (2, $number, @listofnumbers);

  17. Regular expressions:Pattern matching $str = "The large swirls are eddies in the Gulf."; $str =~ m/die/ ; #true $str =~ /gulf/ ; #false $str !~ /gulf/i ; #false $_ = $str; /^the/ ; #false • Modifiers: g: match globally i: case-insensitive matching m: multi-line o: compile once s: single-line x: extended RE

  18. Regular expressions:Basic elements \ Quote next metacharacter . Any character ^ Start of line $ End of line \b \B (Non-)Word boundary \w \W (Non-)Word character \s \S (Non-)Whitespace \d \D (Non-)Digit \t Tab \n Newline $var Match contents of variable ${var} To explicitly delimit variables

  19. Regular expressions:Basic elements | Alternation () Grouping [] Character class [^] Negative character class * Match 0 or more + Match 1 or more ? Match 1 or 0 {n} Match exectly n {n,} Match n or more {n,m} Match n or more, but less than m *? +? ?? {}? Reverse 'greedy' behaviour

  20. Regular expressions:Extracting matched patterns if ($match = ($string =~ /\d+/)) { print $match } ($a, $b) = /(\w)\s(\w)/; @mygroups = (`groups` =~ /\b(\w+)\b/g); /setenv\s*(\w+)\s*(\w+)/; $vars{ nmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm /mmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmmm /$1} = $2;

  21. Regular expressions:Substitution and translation • Substitution: $str =~ s/green/blue/g; s/\b(.)(.*)(.)\b/\3\2\1/g; s/(\d+)/1 + $1/eg; • Translation: tr/abc/ABC/; tr/A-Z/QWERTYUIOPASDFGHJKLZXCVBNM/;

  22. Regular expressions:Some example REs /\/\s*0*\.0*/ ; /[a-z]['")]*[.!?]+['")]*\s/ ; s|/usr/bin|/usr/local/bin| ; $count = s/Mister\b/Mr./g ; s/\d+/$&*2/eg ; s/(\$\w+)/$1/eeg ; $program =~ s { /\* # Match opening delimiter. .*? # Match minimal characters. \*/ # Match closing delimiter. } []gsx;

  23. Some common Perl functions:Strings • length $l = length $string; $l = length; #uses $_ • split @list = split /[,\s]/, $string, 10; ($name, $value) = split /=/; • substr $piece = substr $string, 2, 10; • chop & chomp $c = chop $string; chomp @lines; $/ = ' '; chomp; • pack & unpack

  24. Some common Perl functions:Lists • push & pop push @list, $item; $num = push @list, @items; $item = pop @list; • shift & unshift $item = shift @list; unshift @list, $item; • sort @sorted = sort @list; print sort {$a <=> $b} @list; • splice @sublist = splice @list, 2, 5; splice @list, $off, $len, @newitems;

  25. Some common Perl functions:Miscellaneous • time & localtime ($sec,$min,$hour,$mday,$mon,$year, $wday,$yday,$isdst) = localtime time; $now = localtime; # "Thu Oct 13 04:54:34 1994" • rand & srand srand time; $x = rand 10;

  26. A glimpse of someadvanced features • References and complex data structures • Formats • POD: plain old documentation • Modules • Perl/Tk and Perl/CGI • Databases • OO Perl

  27. Conclusion:When to use Perl • Advanced "shell scripts". • Process management. • Writing quick routines to batch process files or access databases. • Anything involving a lot of string handling (ASCII or binary). • CGI and other web-programming.

  28. Conclusion:When not to use Perl • Heavy computations. • Large applications.

  29. Conclusion:Further resources • Books: • "Programming Perl" 2/e, Larry Wall, Tom Christiansen & Randal Schwartz. (The camel book.) • "Learning Perl" 2/e, Randal Schwartz, Tom Christiansen & Larry Wall. (The llama book.) • "Perl in a Nutshell", Ellen Siever, Stephen Spainhour & Nathan Patwardhan. • "Advanced Perl Programming", Sriram Srinivasan.

  30. Conclusion:Further resources • Web-sites: • Perl Core Documentation: http://www.perldoc.com/ • Nik Silver's Perl Tutorial: http://www.comp.leeds.ac.uk/nik/start.html

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